Conventional electronic automotive horns employ an electromagnet which, when energized, produces a magnetic field. The magnetic field induces magnetism in a stud, or pole, which is commonly connected through a horn housing and a diaphragm to an armature, positioned within the coil. The stud, which is also positioned within the coil has a air gap from the armature which, as is known in the art, must be precisely set within predetermined tolerances in order to achieve a sound of desirable quality and frequency.
Various approaches have been taken in setting the appropriate air gap during manufacturing of the horn. One such method, as shown in U.S. Pat. No. 3,846,792 (Haigh) turns a cap which is fitted together with mating cylindrical surfaces to a base, until a diaphragm contacts a core. The cap is then turned in the opposite direction until the contact stops, thus setting an appropriate distance between the diaphragm and the core. In U.S. Pat. No. 4,135,473 (Frigo), an air gap is established by jaws which deform the horn casing thereby moving the core relative to the armature. Such a method, however, requires that the jaws and the casing are appropriately aligned. In addition, the method does not account for machining tolerances.
An adjusting cap is used to establish an air gap in U.S. Pat. No. 4,717,906 (Smith) between an armature and a shank. The cap compresses a housing wall to position the shank with respect to the armature. U.S. Pat. No. 4,361,952 (Neese) discloses a similar air gap adjusting method. Both the Smith and Neese methods require, however, measurement of the horn housing relative to the housing diaphragm mounting surface, which results in additional time, as well as apparatus, and are unsuited for large scale manufacturing operations.